The present invention is concerned generally with electronics and more specifically with communication systems. Even more specifically, the invention is considered with a multinode communication system using information packets to pass information from one node to a remote node through a series of intermediate transmissions between the given node and at least one of its predefined neighbors.
The present invention relates to skywave communication systems. By skywave, we mean that communication which is supported by ionized regions above the earth. Such communication is characteristic of high frequency (HF), and may also occur at even higher frequencies. One such higher frequency band is typically designated as very high frequency (VHF).
The frequencies supported by the medium, vary with time. General tendencies over long periods (daily, yearly, and solar cycle periods) are known, but short term variations, over a few minutes or a few hours occur in an apparently random fashion.
Adaptive TDMA (time division multiple access) communication systems have been previously designed which dynamically maintain potentially different frequencies between nodes of the communication system using a process of communicating the quality of received signals between the nodes and storing this information so that an optimum frequency band can be selected, whereby, whenever signal quality deteriorates, an alternate frequency can be selected to provide continued communications. An example of such a system is described in U.S. Pat. No. 4,937,822, dated Jun. 26, 1990, and incorporated herein by reference.
The system outlined in the referenced patent utilized a connectivity phase which could only start a connectivity process at predefined time intervals throughout the day. The connectivity process required checking each of a number of prospective frequencies before deciding which signal would be appropriate to use in initial communications. Thus, even under the best propagation conditions, there would be times when a start-up would be attempted immediately after the occurrence of a predefined start-time interval and would necessitate a lengthy delay interval while all frequencies were checked and subsequent communication frequency(ies) were selected.
The long start-up requirement described in the above referenced U.S. Patent was addressed in U.S. Pat. No. 5,204,855, dated Apr. 20, 1993, and U.S. Pat. No. 5,204,856, dated Apr. 20, 1993, both incorporated herein by reference. With knowledge that each communication node operated from a precise clock and utilized a common connectivity algorithm, such that each node knows exactly what frequency would be attempted by a given neighbor node if that neighbor node were to be transmitting at that time. Thus, each operating node continuously checks a set of frequencies for receipt of signals from other nodes, whether or not the other nodes are operating at that time, to see if start-up is commencing. Since each of the nodes transmits unique preamble signals that identify the source of the transmission, when a given node receives such a transmission identifiable as belonging to a previously assigned neighbor, that node hereforth intransmissions to the node coming on line provides information as to the frequency of the first heard signal as long as the quality of the signal meets minimum standards of quality. As soon as both of the nodes have heard a signal from the other of the stated minimum quality, a connection is declared, and traffic data is transmitted as appropriate. The system continues to search for better frequencies (higher quality) to use in future traffic situations but in the meantime, traffic data can be delivered.
Obviously, the selection of a frequency or frequencies that exhibit superior standards of quality, is of paramount importance. The present invention is directed to the evaluation process of attempted frequencies in order to best determine which frequency will provide superior performance.